A technology for maintaining consistency of data stored in an information processing system is known. As this technology, for example, there is a method for surely maintain the order of processes when data is updated.
Further, as one of the methods to store data, a key value store is known. In the key value store, data (value) is stored with a key to identify a record where the data is to be stored. In general, the key value store is used in a client server system, a cloud system or the like via a network. In other words, it is used in a system that includes a server device that stores data in the key value store and a client device that accesses to the key value store. The client device reads data in the key value store by specifying a key. Further, the client device updates the key value store using a pair of the key and the data (value).
However, it is difficult to maintain data consistency in the key value store, different from transactional database. For example, the key value store cannot arbitrate the order of simultaneous accesses from the client devices in parallel. Further, the key value store simply proceeds processes even when the order of access requests transmitted from the client devices is exchanged due to a delay or failure of a network.